The present invention relates to transmission systems for video and data signals. More specifically the invention relates to a low noise adapter device which is suitable for coupling testing equipment to a balanced two wire unshielded twisted pair for testing same.
Cable television (CATV) is transmitted over 75 ohm coaxial cable. Channels 2-60 are transmitted on the cable at frequencies ranging from 5 to 500 MHz. Many homes and commercial buildings have previously installed telephone cables consisting of unshielded twisted pairs. The standard unshielded twisted pairs (UTP) of telephone cables have a characteristic impedance of 100 ohms. It is often convenient to utilize this cable for transmission of video signals. Perhaps more significantly, UTP cable may also be utilized for transmission of computer data signals. Currently such cable and applications, such as local area networks, transmit computer data in the 20 to 30 MHz range. In the foreseeable future such transmission speeds on such cable may exceed 100 MHz.
There are difficulties associated with using the unshielded twisted pair cable for the above, particularly the transmission of CATV signals. Any attempt to utilize the UTP cable with unbalanced CATV signals or other unbalanced signals will result in unacceptable radiation and attenuation of the signals. Techniques such as shown in U.S. Pat. Nos. 5,633,614 and 5,495,212 also assigned to the owner of the instant invention, provide generally acceptable matching of the CATV coaxial cable with the UTP cable.
It is often useful or necessary to measure the balance and other characteristics of UTP cable particularly with reference to the potential usage of such cable for carrying CATV or data signals. Appropriate test equipment for performing such measurements, including network analyzers and signal generators, generally have a characteristic impedance of 50 ohms. Thus, attempts to make any quality measurements of the cable or other associated equipment such as connectors is impossible without suitably matching the test equipment characteristic impedance with that the UTP cable. Heretofore baluns and adapters suitable for such coupling had a restricted frequency range, for example up to 100 MHz. An adapter device is needed which offers high performance low noise coupling up to and beyond 350 MHz.